The Forerunner 35t offers a built-in indoor activity profiles, allowing the device to be used indoors or without GPS. Starting the timer and using the lap key would allow the device to function like a more traditional stopwatch.
I am not aware of any video that specifically shows the lap function of the Forerunner 35. We have posted several overview and pairing videos in the sticky thread at the top of this forum. When the lap key is enabled the lower left button is used to manually mark a split/lap. When the lap key is pressed, the split/lap is displayed on the screen of the watch breifly showing the lap number and time for that lap. After about 3 seconds (or a press of the down button) the screen will go back to the normal data fields. After uploading the activity to Garmin Connect the splits/laps can be viewed individually.